Among polyethers which have reactive silicon groups in the molecules thereof is, for example, a polyether produced and distributed by Kaneka Corp. under a trade name of Kaneka MS polymer. Japanese Patents Laid-Open Nos. 8-231707, 8-176429 and 8-295804, and the like disclose that when the total content of the ionic impurities such as sodium, cobalt, zinc and chlorine is larger than 50 ppm in a reactive silicon group-containing polyether obtained by use of a polyether as a starting material which is obtained by polymerization with a double metal cyanide complex catalyst, the storage stabilities and the like of the reactive silicon group-containing polyether and compositions derived therefrom are lowered, and hence the total content of the ionic impurities is preferably 50 ppm or less, more preferably 30 ppm or less, and furthermore preferably 20 ppm or less. However, even if the total content of the ionic impurities is decreased to 20 ppm or less, a problem arises that compositions containing such a reactive silicon group-containing polyether may cause red coloration, and the problem still remains unsolved. Reactive silicon group-containing compositions are used as sealants and adhesives, and hence the external appearance of such compositions is preferably colorless and transparent or pale in color and transparent. Accordingly, there is a problem that significant red coloration, if any, restricts the application of these compositions to the above described purposes.